You wouldn’t know it from this happy snap, but these parents live with the daily fear their youngest daughter could die from a fit brought on by any sudden noise.

Even a sneeze could spark a killer convulsion for Blisse Mellens and her family have to live in near silence to make sure the two-year-old is never startled.

Parents Laura, 27, and Ashley, 31, and eight-year-old sister Nevaeh tiptoe around their home to avoid triggering a fit in the youngster who has rare conditions that stops her brain developing properly.

Laura said: “We have to think about every noise we make in the house every day.

“If you sneeze or cough you can make Blisse fit. You have got to be absolutely quiet all the time.

“It is a startle reflex. If someone gets up suddenly or she hears your shoe on the floor it startles her.

"I’ve even had to put my house phone on the low setting, because the ring can make her fit.”

Blisse has polymicrogyria and periventricular nodular heterotopia which both affect the way the brain grows.

Apart from the fits, the conditions also mean she cannot walk or talk.

Many of the convulsions could be fatal but most cause Blisse to slip into a trance-like state that lasts about 20 seconds.

The worst are called tonic-clonic seizures when she turns blue and stops breathing.

There is an alarm in the family home at Barry, near Cardiff, which is triggered if Blisse fits during the night in bed.

Her parents have to take turns to look after her while the other sleeps.

Laura said: “We have learned to be able to manage without ringing the ambulance. But it is ­devastating.

"The doctors have told us she is probably never going to speak or sit or walk.

“We would love to hear what her voice is like and things like that but we have accepted that is not going to happen.

"I communicate with her with her eyes. I can tell by the expressions on her face whether she is happy or sad.

“It has been very difficult for Nevaeh. She finds it hard that her little sister can’t talk and play like other children.

“But slowly she’s learning to understand and she’s been a brilliant big sister.”

Doctors say Blisse may live to adulthood but is not likely to survive past 40.

Laura added: “No one knows why this has happened. The doctors think I might have had some sort of infection during my pregnancy.

"A year ago I had expectations of what Blisse might be able to do.

“But all that I want to see now is my little girl smile. Her smile lights up her face.”